Method for operating in power saving mode in wireless LAN system and apparatus therefor

ABSTRACT

According to an embodiment of the present invention, a method in which a station (STA) operates in a power saving (PS) mode in a wireless LAN system supporting a high efficiency physical layer protocol data unit (HE PPDU) comprises the steps of: receiving a trigger frame for allocating a resource for uplink multi-user (UL MU) PPDU transmission; and determining whether the STA shifts into a doze state, on the basis of the trigger frame, wherein the STA determines to shift into the doze state when the resource is not allocated to the STA through the trigger frame, and a time interval in which the STA operates in the doze sate may be determined on the basis of a PS mode field included in the trigger frame.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2016/005182, filed on May 16, 2016, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 62/161,275,filed on May 14, 2015, No. 62/170,701, filed on Jun. 4, 2015, No.62/276,242, filed on Jan. 8, 2016, all of which are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to a method of operating in a power savingmode in a wireless Local Area Network (LAN) system and, moreparticularly, to a method of operating in a power saving mode based on areceived frame and an apparatus therefor.

BACKGROUND ART

Standards for Wireless Local Area Network (WLAN) technology have beendeveloped as Institute of Electrical and Electronics Engineers (IEEE)802.11 standards. IEEE 802.11a and b use an unlicensed band at 2.4 GHzor 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides atransmission rate of 54 Mbps by applying Orthogonal Frequency DivisionMultiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmissionrate of 300 Mbps for four spatial streams by applying Multiple InputMultiple Output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidthof up to 40 MHz and, in this case, provides a transmission rate of 600Mbps.

The above-described WLAN standards have evolved into IEEE 802.11ac thatuses a bandwidth of up to 160 MHz and supports a transmission rate of upto 1 Gbits/s for 8 spatial streams and IEEE 802.11ax standards are underdiscussion.

DETAILED DESCRIPTION OF THE INVENTION Technical Problems

It is a technical object of the present invention to provide a method ofefficiently operating in a power saving mode by a third party station(STA) receiving a frame in a wireless LAN system supporting aHigh-Efficiency Physical Layer Protocol Data Unit (HE PPDU), and anapparatus therefor.

The present invention is not limited to what has been describedhereinabove and other technical objects may be derived from embodimentsof the present invention.

Technical Solutions

According to an aspect of the present invention, provided herein is amethod of operating in a power saving (PS) mode by a station (STA) in awireless Local Area Network (LAN) system supporting a High EfficiencyPhysical Layer Protocol Data Unit (HE PPDU), including receiving a frameincluding duration information; setting a Network Allocation Vector(NAV) based on the duration information; and determining whether totransition to the PS mode, wherein the frame further includesinformation indicating whether the duration information included in theframe is to be changed, and the determining whether to transition to thePS mode includes determining that the STA should be maintained in awake-up state when the information indicates that the durationinformation is to be changed.

The information indicating whether the duration information is to bechanged may be transmitted through an HE preamble or a Media AccessControl (MAC) Protocol Data Unit (MPDU) included in the frame.

The determining whether to transition to the PS mode may includedetermining to transition to the PS mode when the information indicatesthat the duration information is not to be changed.

The determining whether to transition to the PS mode may includedetermining to transition to the PS mode when the frame is received froma Basic Service Set (BSS) to which the STA belongs.

The determining whether to transition to the PS mode may includedetermining to maintain the wake-up state, when the informationindicates that the duration information is not be changed but downlinkdata which is to be received by the STA is present.

The duration information may be indicated by a transmission opportunity(TXOP) duration included in a High-Efficiency Signal A (HE-SIG A) fieldof the frame or a duration field included in a Media Access Control(MAC) header of the frame.

The method may further include receiving another frame including changedduration information and updating the NAV based on the changed durationinformation included in the other frame.

According to another aspect of the present invention, provided herein isa method of operating in a power saving (PS) mode by a station (STA) ina wireless Local Area Network (LAN) system supporting a High EfficiencyPhysical Layer Protocol Data Unit (HE PPDU), including receiving atrigger frame for allocating a resource for transmission of an UplinkMulti-User (UL MU) PPDU; and determining whether to transition to a dozestate based on the trigger frame, wherein the STA determines totransition to the doze state when the resource is not allocated to theSTA through the trigger frame, and a time during which the STA operatesin the doze state is determined based on a PS mode field included in thetrigger frame.

According to still another aspect of the present invention, providedherein is a station (STA) for operating in a power saving (PS) mode in awireless Local Area Network (LAN) system supporting High EfficiencyPhysical Layer Protocol Data Unit (HE PPDU), including a receiverconfigured to receive a trigger frame for allocating a resource fortransmission of an Uplink Multi-User (UL MU) PPDU; and a processorconfigured to determine whether to transition to a doze state based onthe trigger frame, wherein the processor determines to transition to thedoze state when a resource is not allocated to the STA through thetrigger frame, and a time during which the STA operates in the dozestate is determined based on a PS mode field included in the triggerframe.

The PS mode field may indicate whether the STA should operate in thedoze state during an entire transmission opportunity (TXOP) durationindicated by the trigger frame or the STA should operate in the dozestate only during a duration corresponding to the UL MU PPDU transmittedbased on the trigger frame.

If the PS mode field indicates that the STA should operate in the dozestate only during the duration corresponding to the UL MU PPDU, the STAmay transition to an awake state after the duration corresponding to theUL MU PPDU in order to receive other trigger frames transmitted afterthe duration corresponding to the UL MU PPDU.

If the PS mode field indicates that the STA should operate in the dozestate during the entire TXOP duration, the STA may assume that aresource is not allocated to the STA even by other trigger framestransmitted after the duration corresponding to the UL MU PPDU.

The time during which the STA operates in the doze state may be any oneof a transmission opportunity (TXOP) duration indicated by the triggerframe, a duration for the UL MU PPDU, and the sum of the duration forthe UL MU PPDU and a duration for an acknowledgement response frame forthe UL MU PPDU.

The PS mode field may indicate whether a group of STAs to which aresource is allocated is identically maintained or the group of the STAsis changed, during the TXOP duration.

Advantageous Effects

According to an embodiment of the present invention, when framereception is needed later, since a third party STA can maintain awake-up state without transitioning to a power saving mode, NAVmanagement can be accurately performed and the STA operates in a powersaving mode during a duration in which the STA cannot access a channel,so that power can be efficiently managed.

Technical effects that are not described above may be derived fromembodiments of the present invention.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a configuration of a wireless LANsystem.

FIG. 2 illustrates another example of a configuration of a wireless LANsystem.

FIG. 3 illustrates a general link setup procedure.

FIG. 4 illustrates a backoff procedure.

FIG. 5 is an explanatory diagram of a hidden node and an exposed node.

FIG. 6 is an explanatory diagram of RTS and CTS.

FIGS. 7 to 9 are explanatory diagrams of operation of an STA that hasreceived TIM.

FIG. 10 is an explanatory diagram of an exemplary frame structure usedin an IEEE 802.11 system.

FIG. 11 illustrates a contention free (CF)-END frame.

FIG. 12 illustrates an example of an HE PPDU.

FIG. 13 illustrates another example of the HE PPDU.

FIG. 14 illustrates another example of the HE PPDU.

FIG. 15 illustrates another example of the HE PPDU.

FIG. 16 illustrates another example of the HE PPDU.

FIGS. 17 and 18 illustrating an HE-SIG B padding method.

FIG. 19 is an explanatory diagram of uplink multi-user transmissionaccording to an embodiment of the present invention.

FIG. 20 illustrates a trigger frame format according to an embodiment ofthe present invention.

FIG. 21 illustrates an example of NAV setting.

FIG. 22 illustrates an example of TXOP truncation.

FIG. 23 illustrates a value of a TXOP duration indicated by HE-SIG A anda value of a MAC duration indicated by a MAC header.

FIG. 24 illustrates over-protection of a TXOP duration.

FIG. 25 illustrates TXOP truncation according to an embodiment of thepresent invention.

FIG. 26 illustrates an exemplary transmission of multiple UL MU framesin one TXOP.

FIG. 27 illustrates another exemplary transmission of multiple UL MUframes in one TXOP.

FIG. 28 illustrates a doze state of an STA based on a trigger frameaccording to an embodiment of the present invention.

FIGS. 29 and 30 illustrate PS mode setting according to embodiments ofthe present invention.

FIG. 31 illustrates a PS mode operating method according to anembodiment of the present invention.

FIG. 32 is an explanatory diagram of apparatuses according to anembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the present invention.

The following detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. In some instances, knownstructures and devices are omitted or are shown in block diagram form,focusing on important features of the structures and devices, so as notto obscure the concept of the present invention.

As described before, the following description is given of a method andapparatus for increasing a spatial reuse rate in a Wireless Local AreaNetwork (WLAN) system. To do so, a WLAN system to which the presentinvention is applied will first be described in detail.

FIG. 1 is a diagram illustrating an exemplary configuration of a WLANsystem.

As illustrated in FIG. 1, the WLAN system includes at least one BasicService Set (BSS). The BSS is a set of STAs that are able to communicatewith each other by successfully performing synchronization.

An STA is a logical entity including a physical layer interface betweena Media Access Control (MAC) layer and a wireless medium. The STA mayinclude an AP and a non-AP STA. Among STAs, a portable terminalmanipulated by a user is the non-AP STA. If a terminal is simply calledan STA, the STA refers to the non-AP STA. The non-AP STA may also bereferred to as a terminal, a Wireless Transmit/Receive Unit (WTRU), aUser Equipment (UE), a Mobile Station (MS), a mobile terminal, or amobile subscriber unit.

The AP is an entity that provides access to a Distribution System (DS)to an associated STA through a wireless medium. The AP may also bereferred to as a centralized controller, a Base Station (BS), a Node-B,a Base Transceiver System (BTS), or a site controller.

The BSS may be divided into an infrastructure BSS and an Independent BSS(IBSS).

The BSS illustrated in FIG. 1 is the IBSS. The IBSS refers to a BSS thatdoes not include an AP. Since the IBSS does not include the AP, the IBSSis not allowed to access to the DS and thus forms a self-containednetwork.

FIG. 2 is a diagram illustrating another exemplary configuration of aWLAN system.

BSSs illustrated in FIG. 2 are infrastructure BSSs. Each infrastructureBSS includes one or more STAs and one or more APs. In the infrastructureBSS, communication between non-AP STAs is basically conducted via an AP.However, if a direct link is established between the non-AP STAs, directcommunication between the non-AP STAs may be performed.

As illustrated in FIG. 2, the multiple infrastructure BSSs may beinterconnected via a DS. The BSSs interconnected via the DS are calledan Extended Service Set (ESS). STAs included in the ESS may communicatewith each other and a non-AP STA within the same ESS may move from oneBSS to another BSS while seamlessly performing communication.

The DS is a mechanism that connects a plurality of APs to one another.The DS is not necessarily a network. As long as it provides adistribution service, the DS is not limited to any specific form. Forexample, the DS may be a wireless network such as a mesh network or maybe a physical structure that connects APs to one another.

Layer Architecture

An operation of an STA in a WLAN system may be described from theperspective of a layer architecture. A processor may implement the layerarchitecture in terms of device configuration. The STA may have aplurality of layers. For example, the 802.11 standards mainly deal witha MAC sublayer and a PHY layer on a Data Link Layer (DLL). The PHY layermay include a Physical Layer Convergence Protocol (PLCP) entity, aPhysical Medium Dependent (PMD) entity, and the like. Each of the MACsublayer and the PHY layer conceptually includes management entitiescalled MAC sublayer Management Entity (MLME) and Physical LayerManagement Entity (PLME). These entities provide layer managementservice interfaces through which a layer management function isexecuted.

To provide a correct MAC operation, a Station Management Entity (SME)resides in each STA. The SME is a layer independent entity which may beperceived as being present in a separate management plane or as beingoff to the side. While specific functions of the SME are not describedin detail herein, the SME may be responsible for collectinglayer-dependent states from various Layer Management Entities (LMEs) andsetting layer-specific parameters to similar values. The SME may executethese functions and implement a standard management protocol on behalfof general system management entities.

The above-described entities interact with one another in variousmanners. For example, the entities may interact with one another byexchanging GET/SET primitives between them. A primitive refers to a setof elements or parameters related to a specific purpose. AnXX-GET.request primitive is used to request a predetermined MIBattribute value (management information-based attribute information). AnXX-GET.confirm primitive is used to return an appropriate MIB attributeinformation value when the Status field indicates “Success” and toreturn an error indication in the Status field when the Status fielddoes not indicate “Success”. An XX-SET.request primitive is used torequest setting of an indicated MIB attribute to a predetermined value.When the MIB attribute indicates a specific operation, the MIB attributerequests the specific operation to be performed. An XX-SET.confirmprimitive is used to confirm that the indicated MIB attribute has beenset to a requested value when the Status field indicates “Success” andto return an error condition in the Status field when the Status fielddoes not indicate “Success”. When the MIB attribute indicates a specificoperation, it confirms that the operation has been performed.

Also, the MLME and the SME may exchange various MLME_GET/SET primitivesthrough an MLME Service Access Point (MLME_SAP). In addition, variousPLME GET/SET primitives may be exchanged between the PLME and the SMEthrough a PLME_SAP, and exchanged between the MLME and the PLME throughan MLME-PLME_SAP.

Link Setup Process

FIG. 3 is a flowchart explaining a general link setup process accordingto an exemplary embodiment of the present invention.

In order to allow an STA to establish link setup on the network as wellas to transmit/receive data over the network, the STA must perform suchlink setup through processes of network discovery, authentication, andassociation, and must establish association and perform securityauthentication. The link setup process may also be referred to as asession initiation process or a session setup process. In addition, anassociation step is a generic term for discovery, authentication,association, and security setup steps of the link setup process.

Link setup process is described referring to FIG. 3.

In step S510, STA may perform the network discovery action. The networkdiscovery action may include the STA scanning action. That is, STA mustsearch for an available network so as to access the network. The STAmust identify a compatible network before participating in a wirelessnetwork. Here, the process for identifying the network contained in aspecific region is referred to as a scanning process.

The scanning scheme is classified into active scanning and passivescanning

FIG. 3 is a flowchart illustrating a network discovery action includingan active scanning process. In the case of the active scanning, an STAconfigured to perform scanning transmits a probe request frame and waitsfor a response to the probe request frame, such that the STA can movebetween channels and at the same time can determine which Access Point(AP) is present in a peripheral region. A responder transmits a proberesponse frame, acting as a response to the probe request frame, to theSTA having transmitted the probe request frame. In this case, theresponder may be an STA that has finally transmitted a beacon frame in aBSS of the scanned channel. In BSS, since the AP transmits the beaconframe, the AP operates as a responder. In IBSS, since STAs of the IBSSsequentially transmit the beacon frame, the responder is not constant.For example, the STA, that has transmitted the probe request frame atChannel #1 and has received the probe response frame at Channel #1,stores BSS-associated information contained in the received proberesponse frame, and moves to the next channel (for example, Channel #2),such that the STA may perform scanning using the same method (i.e.,probe request/response transmission/reception at Channel #2).

Although not shown in FIG. 3, the scanning action may also be carriedout using passive scanning AN STA configured to perform scanning in thepassive scanning mode waits for a beacon frame while simultaneouslymoving from one channel to another channel. The beacon frame is one ofmanagement frames in IEEE 802.11, indicates the presence of a wirelessnetwork, enables the STA performing scanning to search for the wirelessnetwork, and is periodically transmitted in a manner that the STA canparticipate in the wireless network. In BSS, the AP is configured toperiodically transmit the beacon frame. In IBSS, STAs of the IBSS areconfigured to sequentially transmit the beacon frame. If each STA forscanning receives the beacon frame, the STA stores BSS informationcontained in the beacon frame, and moves to another channel and recordsbeacon frame information at each channel. The STA having received thebeacon frame stores BSS-associated information contained in the receivedbeacon frame, moves to the next channel, and thus performs scanningusing the same method.

In comparison between the active scanning and the passive scanning, theactive scanning is more advantageous than the passive scanning in termsof delay and power consumption.

After the STA discovers the network, the STA may perform theauthentication process in step S520. The authentication process may bereferred to as a first authentication process in such a manner that theauthentication process can be clearly distinguished from the securitysetup process of step S540.

The authentication process may include transmitting an authenticationrequest frame to an AP by the STA, and transmitting an authenticationresponse frame to the STA by the AP in response to the authenticationrequest frame. The authentication frame used for authenticationrequest/response may correspond to a management frame.

The authentication frame may include an authentication algorithm number,an authentication transaction sequence number, a state code, a challengetext, a Robust Security Network (RSN), a Finite Cyclic Group (FCG), etc.The above-mentioned information contained in the authentication framemay correspond to some parts of information capable of being containedin the authentication request/response frame, may be replaced with otherinformation, or may include additional information.

The STA may transmit the authentication request frame to the AP. The APmay decide whether to authenticate the corresponding STA on the basis ofinformation contained in the received authentication request frame. TheAP may provide the authentication result to the STA through theauthentication response frame.

After the STA has been successfully authenticated, the associationprocess may be carried out in step S530. The association process mayinvolve transmitting an association request frame to the AP by the STA,and transmitting an association response frame to the STA by the AP inresponse to the association request frame.

For example, the association request frame may include informationassociated with various capabilities, a beacon listen interval, aService Set Identifier (SSID), supported rates, supported channels, RSN,mobility domain, supported operating classes, a TIM (Traffic IndicationMap) broadcast request, interworking service capability, etc.

For example, the association response frame may include informationassociated with various capabilities, a state code, an Association ID(AID), supported rates, an Enhanced Distributed Channel Access (EDCA)parameter set, a Received Channel Power Indicator (RCPI), a ReceivedSignal to Noise Indicator (RSNI), mobility domain, a timeout interval(association comeback time), an overlapping BSS scan parameter, a TIMbroadcast response, a Quality of Service (QoS) map, etc.

The above-mentioned information may correspond to some parts ofinformation capable of being contained in the associationrequest/response frame, may be replaced with other information, or mayinclude additional information.

After the STA has been successfully associated with the network, asecurity setup process may be carried out in step S540. The securitysetup process of Step S540 may be referred to as an authenticationprocess based on Robust Security Network Association (RSNA)request/response. The authentication process of step S520 may bereferred to as a first authentication process, and the security setupprocess of Step S540 may also be simply referred to as an authenticationprocess.

For example, the security setup process of Step S540 may include aprivate key setup process through 4-way handshaking based on anExtensible Authentication Protocol over LAN (EAPOL) frame. In addition,the security setup process may also be carried out according to othersecurity schemes not defined in IEEE 802.11 standards.

Medium Access Mechanism

In the IEEE 802.11-based WLAN system, a basic access mechanism of MediumAccess Control (MAC) is a Carrier Sense Multiple Access with CollisionAvoidance (CSMA/CA) mechanism The CSMA/CA mechanism is referred to as aDistributed Coordination Function (DCF) of IEEE 802.11 MAC, andbasically includes a “Listen Before Talk” access mechanism In accordancewith the above-mentioned access mechanism, the AP and/or STA may performClear Channel Assessment (CCA) for sensing an RF channel or mediumduring a predetermined time interval [for example, DCF Inter-Frame Space(DIFS)], prior to data transmission. If it is determined that the mediumis in the idle state, frame transmission through the correspondingmedium begins. On the other hand, if it is determined that the medium isin the occupied state, the corresponding AP and/or STA does not startits own transmission, establishes a delay time (for example, a randombackoff period) for medium access, and attempts to start frametransmission after waiting for a predetermined time. Through applicationof a random backoff period, it is expected that multiple STAs willattempt to start frame transmission after waiting for different times,resulting in minimum collision.

In addition, IEEE 802.11 MAC protocol provides a Hybrid CoordinationFunction (HCF). HCF is based on DCF and Point Coordination Function(PCF). PCF refers to the polling-based synchronous access scheme inwhich periodic polling is executed in a manner that all reception (Rx)APs and/or STAs can receive the data frame. In addition, HCF includesEnhanced Distributed Channel Access (EDCA) and HCF Controlled ChannelAccess (HCCA). EDCA is achieved when the access scheme provided from aprovider to a plurality of users is contention-based. HCCA is achievedby the contention-free-based channel access scheme based on the pollingmechanism. In addition, HCF includes a medium access mechanism forimproving Quality of Service (QoS) of WLAN, and may transmit QoS data inboth a Contention Period (CP) and a Contention Free Period (CFP).

FIG. 4 is a conceptual diagram illustrating a backoff process.

Operations based on a random backoff period will hereinafter bedescribed with reference to FIG. 4. If the occupy- or busy-state mediumis shifted to an idle state, several STAs may attempt to transmit data(or frame). As a method for implementing a minimum number of collisions,each STA selects a random backoff count, waits for a slot timecorresponding to the selected backoff count, and then attempts to startdata transmission. The random backoff count has a value of a PacketNumber (PN), and may be set to one of 0 to CW values. In this case, CWrefers to a Contention Window parameter value. Although an initial valueof the CW parameter is denoted by CWmin, the initial value may bedoubled in case of a transmission failure (for example, in the case inwhich ACK of the transmission frame is not received). If the CWparameter value is denoted by CWmax, CWmax is maintained until datatransmission is successful, and at the same time it is possible toattempt to start data transmission. If data transmission was successful,the CW parameter value is reset to CWmin. Preferably, CW, CWmin, andCWmax are set to 2^(n)-1 (where n=0, 1, 2, . . . ).

If the random backoff process starts operation, the STA continuouslymonitors the medium while counting down the backoff slot in response tothe decided backoff count value. If the medium is monitored as theoccupied state, the countdown stops and waits for a predetermined time.If the medium is in the idle state, the remaining countdown restarts.

As shown in the example of FIG. 4, if a packet to be transmitted to MACof STA3 arrives at the STA3, the STA3 determines whether the medium isin the idle state during the DIFS, and may directly start frametransmission. In the meantime, the remaining STAs monitor whether themedium is in the busy state, and wait for a predetermined time. Duringthe predetermined time, data to be transmitted may occur in each ofSTA1, STA2, and STA5. If the medium is in the idle state, each STA waitsfor the DIFS time and then performs countdown of the backoff slot inresponse to a random backoff count value selected by each STA. Theexample of FIG. 4 shows that STA2 selects the lowest backoff count valueand STA1 selects the highest backoff count value. That is, after STA2finishes backoff counting, the residual backoff time of STA5 at a frametransmission start time is shorter than the residual backoff time ofSTA1. Each of STA1 and STA5 temporarily stops countdown while STA2occupies the medium, and waits for a predetermined time. If occupying ofthe STA2 is finished and the medium re-enters the idle state, each ofSTA1 and STA5 waits for a predetermined time DIFS, and restarts backoffcounting. That is, after the remaining backoff slot as long as theresidual backoff time is counted down, frame transmission may startoperation. Since the residual backoff time of STA5 is shorter than thatof STA1, STA5 starts frame transmission. Meanwhile, data to betransmitted may occur in STA4 while STA2 occupies the medium. In thiscase, if the medium is in the idle state, STA4 waits for the DIFS time,performs countdown in response to the random backoff count valueselected by the STA4, and then starts frame transmission. FIG. 4exemplarily shows the case in which the residual backoff time of STA5 isidentical to the random backoff count value of STA4 by chance. In thiscase, an unexpected collision may occur between STA4 and STA5. If thecollision occurs between STA4 and STA5, each of STA4 and STA5 does notreceive ACK, resulting in the occurrence of a failure in datatransmission. In this case, each of STA4 and STA5 increases the CW valuetwo times, and STA4 or STA5 may select a random backoff count value andthen perform countdown. Meanwhile, STA1 waits for a predetermined timewhile the medium is in the occupied state due to transmission of STA4and STA5. In this case, if the medium is in the idle state, STA1 waitsfor the DIFS time, and then starts frame transmission after lapse of theresidual backoff time.

STA Sensing Operation

As described above, the CSMA/CA mechanism includes not only a physicalcarrier sensing mechanism in which the AP and/or STA can directly sensethe medium, but also a virtual carrier sensing mechanism. The virtualcarrier sensing mechanism can solve some problems (such as a hidden nodeproblem) encountered in the medium access. For the virtual carriersensing, MAC of the WLAN system can utilize a Network Allocation Vector(NAV). In more detail, by means of the NAV value, the AP and/or STA,each of which currently uses the medium or has authority to use themedium, may inform another AP and/or another STA for the remaining timein which the medium is available. Accordingly, the NAV value maycorrespond to a reserved time in which the medium will be used by the APand/or STA configured to transmit the corresponding frame. AN STA havingreceived the NAV value may prohibit medium access (or channel access)during the corresponding reserved time. For example, NAV may be setaccording to the value of a ‘duration’ field of the MAC header of theframe.

The robust collision detect mechanism has been proposed to reduce theprobability of such collision, and as such a detailed descriptionthereof will hereinafter be described with reference to FIGS. 7 and 8.Although an actual carrier sensing range is different from atransmission range, it is assumed that the actual carrier sensing rangeis identical to the transmission range for convenience of descriptionand better understanding of the present invention.

FIG. 5 is a conceptual diagram illustrating a hidden node and an exposednode.

FIG. 5(a) exemplarily shows the hidden node. In FIG. 5(a), STA Acommunicates with STA B, and STA C has information to be transmitted. InFIG. 5(a), STA C may determine that the medium is in the idle state whenperforming carrier sensing before transmitting data to STA B, under thecondition that STA A transmits information to STA B. Since transmissionof STA A (i.e., occupied medium) may not be detected at the location ofSTA C, it is determined that the medium is in the idle state. In thiscase, STA B simultaneously receives information of STA A and informationof STA C, resulting in the occurrence of collision. Here, STA A may beconsidered as a hidden node of STA C.

FIG. 5(b) exemplarily shows an exposed node. In FIG. 5(b), under thecondition that STA B transmits data to STA A, STA C has information tobe transmitted to STA D. If STA C performs carrier sensing, it isdetermined that the medium is occupied due to transmission of STA B.Therefore, although STA C has information to be transmitted to STA D,the medium-occupied state is sensed, such that the STA C must wait for apredetermined time (i.e., standby mode) until the medium is in the idlestate. However, since STA A is actually located out of the transmissionrange of STA C, transmission from STA C may not collide withtransmission from STA B from the viewpoint of STA A, such that STA Cunnecessarily enters the standby mode until STA B stops transmission.Here, STA C is referred to as an exposed node of STA B.

FIG. 6 is a conceptual diagram illustrating Request To Send (RTS) andClear To Send (CTS).

In order to efficiently utilize the collision avoidance mechanism underthe above-mentioned situation of FIG. 5, it is possible to use a shortsignaling packet such as RTS and CTS. RTS/CTS between two STAs may beoverheard by peripheral STA(s), such that the peripheral STA(s) mayconsider whether information is communicated between the two STAs. Forexample, if STA to be used for data transmission transmits the RTS frameto the STA having received data, the STA having received data transmitsthe CTS frame to peripheral STAs, and may inform the peripheral STAsthat the STA is going to receive data.

FIG. 6(a) exemplarily shows the method for solving problems of thehidden node. In FIG. 6(a), it is assumed that each of STA A and STA C isready to transmit data to STA B. If STA A transmits RTS to STA B, STA Btransmits CTS to each of STA A and STA C located in the vicinity of theSTA B. As a result, STA C must wait for a predetermined time until STA Aand STA B stop data transmission, such that collision is prevented fromoccurring.

FIG. 6(b) exemplarily shows the method for solving problems of theexposed node. STA C performs overhearing of RTS/CTS transmission betweenSTA A and STA B, such that STA C may determine no collision although ittransmits data to another STA (for example, STA D). That is, STA Btransmits an RTS to all peripheral STAs, and only STA A having data tobe actually transmitted can transmit a CTS. STA C receives only the RTSand does not receive the CTS of STA A, such that it can be recognizedthat STA A is located outside of the carrier sensing range of STA C.

Power Management

As described above, the WLAN system has to perform channel sensingbefore STA performs data transmission/reception. The operation of alwayssensing the channel causes persistent power consumption of the STA.There is not much difference in power consumption between the Reception(Rx) state and the Transmission (Tx) state. Continuous maintenance ofthe Rx state may cause large load to a power-limited STA (i.e., STAoperated by a battery). Therefore, if STA maintains the Rx standby modeso as to persistently sense the channel, power is inefficiently consumedwithout special advantages in terms of WLAN throughput. In order tosolve the above-mentioned problem, the WLAN system supports a PowerManagement (PM) mode of the STA.

The PM mode of the STA is classified into an active mode and a PowerSave (PS) mode. The STA is basically operated in the active mode. TheSTA operating in the active mode maintains an awake state. If the STA isin the awake state, the STA may normally operate such that it canperform frame transmission/reception, channel scanning, or the like. Onthe other hand, STA operating in the PS mode is configured to switchfrom the doze state to the awake state or vice versa. STA operating inthe sleep state is operated with minimum power, and the STA does notperform frame transmission/reception and channel scanning.

The amount of power consumption is reduced in proportion to a specifictime in which the STA stays in the sleep state, such that the STAoperation time is increased in response to the reduced powerconsumption. However, it is impossible to transmit or receive the framein the sleep state, such that the STA cannot mandatorily operate for along period of time. If there is a frame to be transmitted to the AP,the STA operating in the sleep state is switched to the awake state,such that it can transmit/receive the frame in the awake state. On theother hand, if the AP has a frame to be transmitted to the STA, thesleep-state STA is unable to receive the frame and cannot recognize thepresence of a frame to be received. Accordingly, STA may need to switchto the awake state according to a specific period in order to recognizethe presence or absence of a frame to be transmitted to the STA (or inorder to receive a signal indicating the presence of the frame on theassumption that the presence of the frame to be transmitted to the STAis decided).

The AP may transmit a beacon frame to STAs in a BSS at predeterminedintervals. The beacon frame may include a traffic indication map (TIM)information element. The TIM information element may include informationindicating that the AP has buffered traffic for STAs associatedtherewith and will transmit frames. TIM elements include a TIM used toindicate a unicast frame and a delivery traffic indication map (DTIM)used to indicate a multicast or broadcast frame.

FIGS. 7 to 9 are conceptual diagrams illustrating detailed operations ofthe STA having received a Traffic Indication Map (TIM).

Referring to FIG. 7, STA is switched from the sleep state to the awakestate so as to receive the beacon frame including a TIM from the AP. STAinterprets the received TIM element such that it can recognize thepresence or absence of buffered traffic to be transmitted to the STA.After STA contends with other STAs to access the medium for PS-Pollframe transmission, the STA may transmit the PS-Poll frame forrequesting data frame transmission to the AP. The AP having received thePS-Poll frame transmitted by the STA may transmit the frame to the STA.STA may receive a data frame and then transmit an ACK frame to the AP inresponse to the received data frame. Thereafter, the STA may re-enterthe sleep state.

As can be seen from FIG. 7, the AP may operate according to theimmediate response scheme, such that the AP receives the PS-Poll framefrom the STA and transmits the data frame after lapse of a predeterminedtime [for example, Short Inter-Frame Space (SIFS)]. In contrast, the APhaving received the PS-Poll frame does not prepare a data frame to betransmitted to the STA during the SIFS time, such that the AP mayoperate according to the deferred response scheme, and as such adetailed description thereof will hereinafter be described withreference to FIG. 8.

The STA operations of FIG. 8 in which the STA is switched from the sleepstate to the awake state, receives a TIM from the AP, and transmits thePS-Poll frame to the AP through contention are identical to those ofFIG. 7. If the AP having received the PS-Poll frame does not prepare adata frame during the SIFS time, the AP may transmit the ACK frame tothe STA instead of transmitting the data frame. If the data frame isprepared after transmission of the ACK frame, the AP may transmit thedata frame to the STA after completion of such contending. STA maytransmit the ACK frame indicating successful reception of a data frameto the AP, and may be shifted to the sleep state.

FIG. 9 shows the exemplary case in which AP transmits DTIM. STAs may beswitched from the sleep state to the awake state so as to receive thebeacon frame including a DTIM element from the AP. STAs may recognizethat multicast/broadcast frame(s) will be transmitted through thereceived DTIM. After transmission of the beacon frame including theDTIM, AP may directly transmit data (i.e., multicast/broadcast frame)without transmitting/receiving the PS-Poll frame. While STAscontinuously maintains the awake state after reception of the beaconframe including the DTIM, the STAs may receive data, and then switch tothe sleep state after completion of data reception.

Frame Structure

FIG. 10 is an explanatory diagram of an exemplary frame structure usedin an IEEE 802.11 system.

A PPDU (Physical Layer Protocol Data Unit) frame format may include anSTF (Short Training Field), an LTF (Long Training Field), a SIG (SIGNAL)field and a data field. The most basic (e.g., non-HT (High Throughput))PPDU frame format may include only an L-STF (Legacy-STF), an L-LTF(Legacy-LTF), a SIG field and a data field.

The STF is a signal for signal detection, AGC (Automatic Gain Control),diversity selection, accurate time synchronization, etc., and the LTF isa signal for channel estimation, frequency error estimation, etc. TheSTF and LTF may be collectively called a PLCP preamble. The PLCPpreamble may be regarded as a signal for OFDM physical layersynchronization and channel estimation.

The SIG field may include a RATE field and a LENGTH field. The RATEfield may include information about modulation and coding rates of data.The LENGTH field may include information about the length of data. Inaddition, the SIG field may include a parity bit, a SIG TAIL bit, etc.

The data field may include a SERVICE field, a PSDU (Physical layerService Data Unit) and a PPDU TAIL bit. The data field may also includepadding bits as necessary. Some bits of the SERVICE field may be usedfor synchronization of a descrambler at a receiving end. The PSDUcorresponds to an MPDU (MAC Protocol Data Unit) defined in the MAC layerand may include data generated/used in a higher layer. The PPDU TAIL bitmay be used to return an encoder to state 0. The padding bits may beused to adjust the length of the data field to a predetermined unit.

The MPDU is defined depending on various MAC frame formats, and a basicMAC frame includes a MAC header, a frame body and an FCS (Frame CheckSequence). The MAC frame may be composed of the MPDU andtransmitted/received through PSDU of a data part of the PPDU frameformat.

The MAC header includes a frame control field, a duration/ID field, anaddress field, etc. The frame control field may include controlinformation necessary for frame transmission/reception. The duration/IDfield may be set to a time to transmit a relevant a relevant frame.

The duration/ID field included in the MAC header may be set to a 16-bitlength (e.g., B0 to B15). Content included in the duration/ID field maydepend on frame type and sub-type, whether transmission is performed fora CFP (contention free period), QoS capability of a transmission STA andthe like. (i) In a control frame corresponding to a sub-type of PS-Poll,the duration/ID field may include the AID of the transmission STA (e.g.,through 14 LSBs) and 2 MSBs may be set to 1. (ii) In frames transmittedby a PC (point coordinator) or a non-QoS STA for a CFP, the duration/IDfield may be set to a fixed value (e.g., 32768). (iii) In other framestransmitted by a non-QoS STA or control frames transmitted by a QoS STA,the duration/ID field may include a duration value defined per frametype. In a data frame or a management frame transmitted by a QoS STA,the duration/ID field may include a duration value defined per frametype. For example, B15=0 of the duration/ID field indicates that theduration/ID field is used to indicate a TXOP duration, and B0 to B14 maybe used to indicate an actual TXOP duration. The actual TXOP durationindicated by B0 to B14 may be one of 0 to 32767 and the unit thereof maybe microseconds (μs). However, when the duration/ID field indicates afixed TXOP duration value (e.g., 32768), B15 can be set to 1 and B0 toB14 can be set to 0. When B14=1 and B15=1, the duration/ID field is usedto indicate an AID, and B0 to B13 indicate one AID of 1 to 2007. Referto the IEEE 802.11 standard document for details of Sequence Control,QoS Control, and HT Control subfields of the MAC header.

The frame control field of the MAC header may include Protocol Version,Type, Subtype, To DS, From DS, More Fragment, Retry, Power Management,More Data, Protected Frame and Order subfields. Refer to the IEEE 802.11standard document for contents of the subfields of the frame controlfield.

FIG. 11 illustrates a CF (contention free)-END frame.

It is assumed that the CF-END frame is transmitted by a non-DMG(directional multi-gigabit, 11ad) STA for convenience of description.The CF-END frame may be transmitted to truncate a TXOP duration.Accordingly, a duration field is set to 0 in the CF-END frame. An RA(Receiver Address) field may be set to a broadcast group address. ABSSID field may be set to an STA address included in a relevant AP.However, in the case of a CF-END frame in a non-HT or non-HT duplicateformat, which is transmitted from a VHT STA to a VHT AP, anIndividual/Group bit of the BSSID field may be set to 1.

Example of HE PPDU structure

A description will be given of examples of an HE PPDU (High EfficiencyPhysical layer Protocol Data Unit) format in a wireless LAN systemsupporting 11ax.

FIG. 12 illustrates an example of the HE PPDU. Referring to FIG. 12, anHE-SIG A (or HE-SIG1) field follows an L-Part (e.g., L-STF, L-LTF,L-SIG) and is duplicated every 20 MHz like the L-Part. The HE-SIG Afield includes common control information (e.g., BW, GI length, BSSindex, CRC, Tail, etc.) for STAs. The HE-SIG A field includesinformation for decoding the HE PPDU and thus information included inthe HE-SIG A field may depend on the format of the HE PPDU (e.g., SUPPDU, MU PPDU, trigger-based PPDU or the like). For example, in the HESU PPDU format, the HE-SIG A field may include at least one of a DL/ULindicator, HE PPDU format indicator, BSS color, TXOP duration, BW(bandwidth), MCS, CP+LTF length, coding information, the number ofstreams, STBC (e.g., whether STBC is used), transmission beamforming(TxBF) information, CRC and Tail. In the case of the HE SU PPDU format,the HE-SIG B field may be omitted. In the HE MU PPDU format, the HE-SIGA field may include at least one of a DL/UL indicator, BSS color, TXOPduration, BW, MCS information of a SIG B field, the number of symbols ofthe SIG B field, the number of HE LTF symbols, indicator indicatingwhether full band MU-MIMO is used, CP+LTF length, transmissionbeamforming (TxBF) information, CRC and Tail. In the HE trigger-basedPPDU format, an HE-SIG A field may include at least one of a formatindicator (e.g., indicating the SU PPDU or trigger-based PPDU), BSScolor, TXOP duration, BW, CRC and Tail.

FIG. 13 illustrates another example of the HE PPDU. Referring to FIG.13, the HE-SIG A may include user allocation information, for example,at least one of an STA ID such as a PAID or a GID, allocated resourceinformation and the number of streams (Nsts), in addition to the commoncontrol information. Referring to FIG. 13, the HE-SIG B (or HE-SIG2) maybe transmitted for each OFDMA allocation. In the case of MU-MIMO, theHE-SIG B is identified by an STA through SDM. The HE-SIG B may includeadditional user allocation information, for example, an MCS, codinginformation, STBC (Space Time Block Code) information and transmissionbeamforming (TXBF) information.

FIG. 14 illustrates another example of the HE PPDU. The HE-SIG B istransmitted following the HE-SIG A. The HE-SIG B may be transmittedthrough the full band on the basis of numerology of the HE-SIG A. TheHE-SIG B may include user allocation information, for example, STA AID,resource allocation information (e.g., allocation size), MCS, the numberof streams (Nsts), coding, STBC and transmission beamforming (TXBF)information.

FIG. 15 illustrates another example of the HE PPDU. The HE-SIG B may beduplicated per predetermined unit channel. Referring to FIG. 15, theHE-SIG B may be duplicated per 20 MHz. For example, the HE-SIG B can betransmitted in such a manner that the same information is duplicated per20 MHz in 80 MHz bandwidth.

An STA/AP which has received the HE-SIG B duplicated every 20 MHz mayaccumulate the received HE-SIG B per 20 MHz channel to improvereliability of HE-SIG B reception.

Since the same signal (e.g., HE-SIG B) is duplicated and transmitted perchannel, the gain of accumulated signals is proportional to the numberof channels over which the signal is duplicated and transmitted toimprove reception performance. In theory, a duplicated and transmittedsignal can have a gain corresponding to 3 dB×(the number of channels)compared to the signal before duplication. Accordingly, the duplicatedand transmitted HE-SIG B may be transmitted with an increased MCS leveldepending on the number of channels through which the HE-SIG B isduplicated and transmitted. For example, if MCS0 is used for the HE-SIGB transmitted without being duplicated, MCS1 can be used for the HE-SIGB duplicated and transmitted. Since the HE-SIG B can be transmitted witha higher MCS level as the number of channels for duplication increases,HE-SIG B overhead per unit channel can be reduced.

FIG. 16 illustrates another example of the HE PPDU. Referring to FIG.16, the HE-SIG B may include independent information per 20 MHz channel.The HE-SIG B may be transmitted in a 1x symbol structure like the Legacypart (e.g., L-STF, L-LTF, L-SIG) and HE-SIG A. Meanwhile, a length of“L-STF+L-LTF+L-SIG+HE-SIGA+HE-SIGB” needs to be identical in allchannels in a wide bandwidth. The HE-SIG B transmitted per 20 MHzchannel may include allocation information about the corresponding band,for example, allocation information per user using the correspondingband, user ID, etc. However, the information of the HE-SIG B may varybetween bands because the respective bands support different numbers ofusers and use different resource block configurations. Accordingly, thelength of the HE-SIG B may be different for respective channels.

FIG. 17 illustrates an HE-SIG B padding method by which lengths beforeHE-STF (e.g., lengths to the HE-SIG B) become identical for respectivechannels. For example, the HE-SIG B may be duplicated by a paddinglength to align HE-SIG B lengths. As illustrated in FIG. 18, the HE-SIGB corresponding to a necessary padding length may be padded to theHE-SIG B from the start (or end) of the HE-SIG B.

According to an example, one HE-SIG B field can be transmitted when thebandwidth does not exceed 20 MHz. When the bandwidth exceeds 20 MHz, 20MHz channels may respectively transmit one of a first type HE-SIG B(referred to hereinafter as HE-SIG B [1]) and a second type HE-SIG B(referred to hereinafter as HE-SIG B [2]). For example, HE-SIG B [1] andHE-SIG B [2] may be alternately transmitted. An odd-numbered 20 MHzchannel may deliver HE-SIG B [1] and an even-numbered 20 MHz channel maydeliver HE-SIG B [2]. More specifically, in the case of a 40 MHzbandwidth, HE-SIG B [1] is transmitted over the first 20 MHz channel andHE-SIG B [2] is transmitted over the second 20 MHz channel. In the caseof an 80 MHz bandwidth, HE-SIG B [1] is transmitted over the first 20MHz channel, HE-SIG B [2] is transmitted over the second 20 MHz channel,the same HE-SIG B [1] is duplicated and transmitted over the third 20MHz channel and the same HE-SIG B [2] is duplicated and transmitted overthe fourth 20 MHz channel. The HE-SIG B is transmitted in a similarmanner in the case of a 160 MHz bandwidth.

As described above, the HE-SIG B can be duplicated and transmitted asthe bandwidth increases. Here, a duplicated HE-SIG B may befrequency-hopped by 20 MHz from a 20 MHz channel over which an HE-SIG Bof the same type is transmitted and transmitted.

HE-SIG B [1] and HE-SIG B [2] may have different content. However,HE-SIG-Bs [1] have the same content. Similarly, HE-SIG Bs [2] have thesame content.

According to an embodiment, HE-SIG B [1] may be configured to includeresource allocation information about only odd-numbered 20 MHz channelsand HE-SIG B [2] may be configured to include resource allocationinformation about only even-numbered 20 MHz channels. According toanother embodiment of the present invention, HE-SIG B [1] may includeresource allocation information about at least part of even-numbered 20MHz channels or HE-SIG B [2] may include resource allocation informationabout at least part of odd-numbered 20 MHz channels.

The HE-SIG B may include a common field and a user-specific field. Thecommon field may precede the user-specific field. The common field andthe user-specific field may be distinguished in a unit of bit(s) insteadof a unit of OFDM symbol(s).

The common field of the HE-SIG B includes information for all STAsdesignated to receive PPDUs in a corresponding bandwidth. The commonfield may include resource unit (RU) allocation information. All theHE-SIG Bs [1] may have the same content and All the HE-SIG Bs [2] mayhave the same content. For example, when four 20 MHz channelsconstituting 80 MHz are classified as [LL, LR, RL, RR], the common fieldof HE-SIG B [1] may include a common block for LL and RL and the commonfield of HE-SIG B [2] may include a common block for LR and RR.

The user-specific field of the HE-SIG B may include a plurality of userfields. Each user field may include information specific to anindividual STA designated to receive PPDUs. For example, the user fieldmay include at least one of an STA ID, MCS per STA, the number ofstreams (Nsts), coding (e.g., indication of use of LDPC), DCM indicatorand transmission beamforming information. However, the information ofthe user field is not limited thereto.

UL MU Transmission

FIG. 19 is an explanatory diagram of an uplink multi-user transmissionsituation according to an embodiment of the present invention.

As described above, an 802.11ax system may employ UL MU transmission. ULMU transmission may be started when an AP transmits a trigger frame to aplurality of STAs (e.g., STA1 to STA4), as illustrated in FIG. 19. Thetrigger frame may include UL MU allocation information. The UL MUallocation information may include at least one of resource position andsize, STA IDs or reception STA addresses, MCS and MU type (MIMO, OFDMA,etc.). Specifically, the trigger frame may include at least one of (i) aUL MU frame duration, (ii) the number of allocations (N) and (iii)information per allocation. The information per allocation may includeinformation per user (Per user Info). The information per allocation mayinclude at least one of an AID (AIDs corresponding to the number of STAsare added in the case of MU), power adjustment information, resource (ortone) allocation information (e.g., bitmap), MCS, the number of streams(Nsts), STBC, coding and transmission beamforming information.

As illustrated in FIG. 19, the AP may acquire TXOP to transmit thetrigger frame through a contention procedure to access media.Accordingly, the STAs may transmit UL data frames in a format indicatedby the AP after SIFS of the trigger frame. It is assumed that the APaccording to an embodiment of the present invention sends anacknowledgement response to the UL data frames through a block ACK (BA)frame.

FIG. 20 illustrates a trigger frame format according to an embodiment.

Referring to FIG. 20, the trigger frame may include at least one of aframe control field, a duration field, an RA (recipient STA address)field, a TA (transmitting STA address) field, a common informationfield, one or more Per User Info fields and FCS (Frame Check Sum). TheRA field indicates the address or ID of a recipient STA and may beomitted according to embodiments. The TA field indicates the address ofa transmitting STA.

The common information field may include at least one of a lengthsubfield, a cascade indication subfield, an HE-SIG A informationsubfield, a CP/LTF type subfield, a trigger type subfield and atrigger-dependent common information subfield. The length subfieldindicates the L-SIG length of a UL MU PPDU. The cascade indicationindicates whether there is transmission of a subsequent trigger framefollowing the current trigger frame. The HE-SIG A information subfieldindicates content to be included in the HE-SIG A of the UL MU PPDU. TheCP/LTF type subfield indicates a CP and HE LTF type included in the ULMU PPDU. The trigger type subfield indicates the type of the triggerframe. The trigger frame may include common information specific to thetype and information per user (Per User Info) specific to the type. Forexample, the trigger type may be set to one of a basic trigger type(e.g., type 0), beamforming report poll trigger type (e.g., type 1),MU-BAR (Multi-user Block Ack Request) type (e.g., type 2) and MU-RTS(multi-user ready to send) type (e.g., type 3). However the trigger typeis not limited thereto. When the trigger type is MU-BAR, thetrigger-dependent common information subfield may include a GCR(Groupcast with Retries) indicator and a GCR address.

The Per User Info field may include at least one of a user ID subfield,an RU allocation subfield, a coding type subfield, an MCS subfield, aDCM (dual sub-carrier modulation) subfield, an SS (spatial stream)allocation subfield and a trigger dependent Per User Info subfield. Theuser ID subfield indicates the AID of an STA which will use acorresponding resource unit to transmit MPDU of the UL MU PPDU. The RUallocation subfield indicates a resource unit used for the STA totransmit the UL MU PPDU. The coding type subfield indicates the codingtype of the UL MU PPDU transmitted by the STA. The MCS subfieldindicates the MCS of the UL MU PPDU transmitted by the STA. The DCMsubfield indicates information about double carrier modulation of the ULMU PPDU transmitted by the STA. The SS allocation subfield indicatesinformation about spatial streams of the UL MU PPDU transmitted by theSTA. In the case of MU-BAR trigger type, the trigger-dependent Per UserInfo subfield may include BAR control and BAR information.

NAV (Network Allocation Vector)

A NAV may be understood as a timer for protecting TXOP of a transmittingSTA (e.g., TXOP holder). An STA may not perform channel access during aperiod in which a NAV configured in the STA is valid so as to protectTXOP of other STAs.

A current non-DMG STA supports one NAV. An STA which has received avalid frame can update the NAV through the duration field of the PSDU(e.g., the duration field of the MAC header). When the RA field of thereceived frame corresponds to the MAC address of the STA, however, theSTA does not update the NAV. When a duration indicated by the durationfield of the received frame is greater than the current NAV value of theSTA, the STA updates the NAV through the duration of the received frame.

FIG. 21 illustrates an example of NAV setting.

Referring to FIG. 21, a source STA transmits an RTS frame and adestination STA transmits CTS frame. As described above, the destinationSTA designated as a recipient through the RTS frame does not set a NAV.Some of other STAs may receive the RTS frame and set NAVs and others mayreceive the CTS frame and set NAVs.

If the CTS frame (e.g., PHY-RXSTART.indication primitive) is notreceived within a predetermined period from a timing when the RTS frameis received (e.g., PHY-RXEND.indication primitive for which MACcorresponds to the RTS frame is received), STAs which have set orupdated NAVs through the RTS frame can reset the NAVs (e.g., 0). Thepredetermined period may be(2*aSIFSTime+CTS_Time+aRxPHYStartDelay+2*aSlotTime). The CTS_Time may becalculated on the basis of the CTS frame length indicated by the RTSframe and a data rate.

Although FIG. 21 illustrates setting or update of a NAV through the RTSframe or CTS frame for convenience, NAV setting/resetting/update may beperformed on the basis of duration fields of various frames, forexample, non-HT PPDU, HT PPDU, VHT PPDU and HE PPDU (e.g., the durationfield of the MAC header of the MAC frame). For example, if the RA fieldof the received MAC frame does not correspond to the address of an STA(e.g., MAC address), the STA may set/reset/update the NAV.

TXOP (Transmission Opportunity) Truncation

FIG. 22 illustrates an example of TXOP truncation.

A TXOP holder STA may indicate to truncate TXOP by transmitting a CF-ENDframe. AN STA can reset the NAV (e.g., set the NAV to 0) upon receptionof a CF-END frame or CF-END+CF-ACK frame.

When an STA that has acquired channel access through EDCA empties atransmission queue thereof, the STA can transmit a CF-END frame. The STAcan explicitly indicate completion of TXOP thereof through transmissionof the CF-END frame. The CF-END frame may be transmitted by a TXOPholder. A non-AP STA that is not a TXOP holder cannot transmit theCF-END frame. A STA which has received the CF-END frame resets the NAVat a time when a PPDU included in the CF-END frame is ended.

Referring to FIG. 22, an STA that has accessed a medium transmits asequence (e.g., RTS/CTS) for NAV setting.

After SIFS, a TXOP holder (or TXOP initiator) and a TXOP respondertransmit and receive PPDUs (e.g., initiator sequence). The TXOP holdertruncates a TXOP by transmitting a CF-END frame when there is no data tobe transmitted within the TXOP.

STAs which have received the CF-END frame reset NAVS thereof and canstart contending for medium access without delay.

As described above, a TXOP duration is set through the duration field ofthe MAC header in the current wireless LAN system. That is, a TXOPholder (e.g., Tx STA) and a TXOP responder (e.g., Rx STA) include wholeTXOP information necessary for transmission and reception of frames induration fields of frames transmitted and received therebetween andtransmit the frames. Third party STAs other than the TXOP holder and theTXOP responder check the duration fields of frames exchanged between theTXOP holder and the TXOP responder and set/update NAVs to defer use ofchannels until NAV periods.

In an 11ax system supporting the HE PPDU, the third party STAs cannotdecode an MPDU included in a UL MU PPDU even when they receive the UL MUPPDU if the UL MU PPDU does not include the HE-SIG B. If the third partySTAs cannot decode the MPDU, the third party STAs cannot acquire TXOPduration information (e.g., duration field) included in the MAC headerof the MPDU. Accordingly, it is difficult to correctly perform NAVsetting/update.

Even when an HE PPDU frame including the HE-SIG B is received, if theHE-SIG B structure is differently encoded per STA and is designed suchthat a STA can read only HE-SIG B content allocated to that STA, thethird party STAs cannot decode a MAC frame (e.g., an MPDU in the HE PPDUcorresponding to other STAs) transmitted and received by other STAs.Accordingly, the third party STAs cannot acquire TXOP information inthis case.

Indication of TXOP Duration Through HE-SIG A

To solve the above-described problems, a method in which an STAtransmits the TXOP duration information in an HE-SIG A field isproposed. As described above, 15 bits (e.g., B0 to B14) in the durationfield of the MAC header may indicate duration information capable ofindicating a maximum of about 32.7 ms (0 to 32767 μs). If the 15-bitduration information included in the duration field of the MAC header istransmitted in the HE-SIG A field, an flax third party STA may correctlyset/update the NAV but signaling overhead of HE-SIG A excessivelyincreases. Although 15 bits in an MPDU for payload transmission in a MAClayer may be relatively small in size, since the HE-SIG A field fortransmitting common control information in a physical layer is compactlydesigned, increase of 15 bits in the HE-SIG A field causes relativelysignificant signaling overhead.

Accordingly, an embodiment of the present invention proposes anefficient TXOP duration indication method of minimizing overhead of theHE-SIG A field. In addition, a frame transmission and receptionoperation based on a newly defined TXOP duration in the HE-SIG A fieldis proposed. Hereinafter, the duration field included in the MAC headermay be referred to as a MAC duration, for convenience.

While it is assumed in an embodiment described hereinbelow that the TXOPduration information is transmitted in the HE-SIG A field, the scope ofthe present invention is not limited thereto and may also be transmittedthrough other parts (e.g., parts of L-SIG, HE-SIG B, HE-SIG C, . . . ,Aggregate-MPDU (A-MPDU), and MPDU). For example, when the TXOP durationinformation is transmitted through the HE-SIG B field, the TXOP durationinformation may be transmitted through a part of transmitting commoninformation (e.g., a common part) of the HE-SIG B field or through anSIG-B content part (e.g., a Per user Info field) transmitted in thefirst (or last) part in the HE-SIG B field.

Hereinafter, the structure of the TXOP duration in the HE-SIG field andembodiments indicating the TXOP duration will be described. A value setas a NAV of a third party STA may be interpreted as a TXOP duration of aTXOP holder/responder. For example, a duration field value is a TXOP forframe transmission and reception in terms of the TXOP holder/responderbut means a NAV value in terms of the third party STA. Accordingly,since an operation in which third party STAs set/update a NAV is to setthe NAV corresponding to the TXOP of the TXOP holder/responder, theoperation in which the third party STAs set/update the NAV may bereferred to as a TXOP setting/update operation, for convenience. Inaddition, the term “TXOP duration” may be simplified to a “duration” ormay be simply referred to as a TXOP. In some cases, the TXOP durationmay be used to refer to a field (e.g., a TXOP duration field in HE-SIGA) in a field or may be used to refer to an actual TXOP duration value.

In embodiments described hereinbelow, indexes are allocated forconvenience of description. Therefore, embodiments described as havingother indexes may be combined to be implemented as one invention or eachof the embodiments described as having other indexes may be implementedas an individual invention.

Embodiment 1

The TXOP duration may be set to 2^(N)−1 (or 2^(N)). For convenience, itis assumed that the TXOP duration is set to 2^(N)−1. The value of N maybe transmitted in the TXOP duration field of HE-SIG A.

For example, if N is 4 bits in size, N has a value of 0 to 15.Therefore, the TXOP duration indicated by N of a 4-bit size may have avalue of 0 to 32767 μs. Unlike this, if the TXOP duration is set toindicate a maximum of 5 ms, N having a value of only 0 to 13 may be usedto indicate the TXOP duration and N having a value of 14 and 15 may beused for other purposes.

The present embodiment exemplifies a method of indicating the TXOPduration using a scheme of X*2^(Y)−1 (e.g., X=1). X and/or Y may bechanged in various manners. Values of X and Y may be transmitted throughthe HE-SIG A field. For example, it may be appreciated that X is a unitor granularity of a TXOP duration value. Since X is variable, it may beappreciated that multiple granularities are used.

Embodiment 2

According to an embodiment of the present invention, the TXOP durationmay be set to X^(Y)−1 (or X^(Y)). For convenience, it is assumed thatthe TXOP duration is set to X^(Y)−1. An STA may transmit the values of Xand Y through the TXOP duration field (e.g., in HE-SIG A).

Assuming that the TXOP duration field transmitted in the HE-SIG A fieldis a total of K bits, n bits (e.g., front n bits) among the K bits mayindicate the value of X and m bits (e.g., back m bits) may indicate thevalue of Y. The n bits may be n most significant bits (MSBs) or n leastsignificant bits (LSBs) and the m bits may be m LSBs or m MSBs. Thevalues of K, m, and n may be set in various manners.

(i) As an example, it is assumed that K=6, n=3, and m=3. X may be aninteger of X∈{2˜9} and Y may be an integer of Y∈{0˜7}. In this case, theTXOP duration has a value of 0 to 4782968 μs.

(ii) As another example, it is assumed that K=5, n=2, and m=3. X may bean integer of X∈{2˜5} and Y may be an integer of Y∈{0˜7}. In this case,the TXOP duration has a value of 0 to 78124 μs. Unlike this, if X is aninteger of X∈{2, 3, 5, 6} and Y is an integer of Y∈{0˜7}, the TXOPduration has a value of 0 to 78124 μs.

(iii) As still another example, it is assumed that K=4, n=1, and m=3. Xmay be an integer of X∈{2, 3} (or X∈{5, 6}) and Y may be an integer ofY∈{0˜7}. Then, the TXOP duration has a value of 0 to 279963 μs.

If it is desired to indicate up to P ms (e.g., 5 ms) through the TXOPduration field (e.g., in HE-SIG A), a combination of (X, Y) having aminimum of X^(Y)−1 among combinations of (X, Y) satisfying X^(Y)−1≥P ms(e.g., 5 ms) may be used to indicate a maximum TXOP duration value andthe other combinations of (X, Y) may not be used.

This embodiment exemplifies a method of indicating the TXOP durationusing a scheme of Z*X^(Y)−1. X, Y, and/or Z may be changed in variousmanners. For example, it may be appreciated that X and/or Z is a unit orgranularity of a TXOP duration value. Since X and/or Z is variable, itmay be appreciated that multiple granularities are used.

Embodiment 3

According to an embodiment of the present invention, the TXOP durationmay be set to X*2^(Y)−1 (or X*2^(Y)). The values of X and Y may betransmitted through the TXOP duration field.

Assuming that the TXOP duration field transmitted in the HE-SIG A fieldis a total of K bits, n bits (e.g., front n bits) among the K bits mayindicate the value of X and m bits (e.g., back m bits) may indicate thevalue of Y. The n bits may be n MSBs or n LSBs and the m bits may be mLSBs or m MSBs. The values of K, m, and n may be set in various manners.

For example, assuming that K=6, n=3, and m=3, X may be one of X∈{1, 5,10, 20, 30, 40, 50, 60} and Y may be an integer of Y∈{0˜7}. In thiscase, the TXOP duration has a value of 0 to 7680 μs.

If it is desired to indicate up to P ms (e.g., 5 ms) through the TXOPduration field (e.g., in HE-SIG A), a combination of (X, Y) having aminimum of X*2^(Y)−1 among combinations of (X, Y) satisfying X*2^(Y)−1≥Pms (e.g., 5 ms) may be used to indicate a maximum TXOP duration valueand the other combinations of (X, Y) may not be used.

This embodiment exemplifies a method of indicating the TXOP durationusing a scheme of X*Z^(Y)−1. X, Y, and/or Z may be variously changed.For example, it may be appreciated that X and/or Z is a unit orgranularity of a TXOP duration value. Since X and/or Z is variable, itmay be appreciated that multiple granularities are used.

Embodiment 4

According to an embodiment, the TXOP duration may be set to other units(e.g., greater units or symbol units) instead of 1 microsecond (μs). Forexample, greater units such as 4 μs, 8 μs, 10 μs, 16 μs, 32 μs, 50 μs,64 μs, 100 μs, 128 μs, 256 μs, 500 μs, 512 μs, 1024 μs, etc. may beused. In this case, the TXOP duration value will be determined as “unit(e.g., 64 μs)*value of TXOP duration field”. For example, when a unit of32 μs is used, the TXOP duration value may be TXOP Duration (1)=32 μs,TXOP Duration (2)=64 μs, TXOP Duration (3)=96 μs, etc.

Meanwhile, it is desirable that the TXOP duration have a maximum valueup to 8 ms. Accordingly, when a single unit is used, the followingoptions of the TXOP duration field may be considered.

-   -   Option 1: A unit of 32 μs as is used and the TXOP duration field        of 8 bits is defined. Herein, a maximum value of the TXOP        duration may be 8192 μs.    -   Option 2: A unit of 64 μs is used and the TXOP duration field of        7 bits is defined. Herein, a maximum value of the TXOP duration        may be 8192 μs.

If the size of the TXOP duration field is set to more than 8 bits (e.g.,to 9 to 11 bits), the following structures of the TXOP duration fieldmay be used.

-   -   Option A-1: 16 μs unit, ˜32 ms, 11 bits    -   Option A-2: 16 μs unit, ˜16 ms, 10 bits    -   Option A-3: 16 μs unit, ˜8 ms, 9 bits    -   Option B-1: 32 μs unit, ˜32 ms, 10 bits    -   Option B-2: 32 μs unit, ˜16 ms, 9 bits    -   Option C-1: 64 μs unit, ˜16 ms, 9 bits

A combination of one or more units (e.g., (16 μs, 512 μs) or (8 μs, 128μs), etc.) may be used.

TXOP Termination/Truncation Method

Meanwhile, according to the above-described embodiments, the TXOPduration field of HE-SIG A may be set to indicate the TXOP durationbased on a relatively large granularity. For example, a duration fieldincluded in a MAC header may be set based on a granularity of 1 μs,whereas the TXOP duration field of HE-SIG A may be set to indicate theTXOP duration based on a granularity greater than 1 μs.

FIG. 23 illustrates the case in which a granularity used in the TXOPduration field of the HE-SIG A field is greater than a granularity usedin the duration field of the MAC header.

In this way, if the TXOP duration is set based on a granularity largerthan the duration field of the MAC header by the TXOP duration field ofthe HE-SIG A field, a time longer than a time used for actual frametransmission may be set as the TXOP duration.

Accordingly, other STAs (e.g., third party STAs) may set a larger NAVthan necessary based on the HE-SIG A field so that a channel cannot beused during a specific time and channel efficiency may be deteriorated.That is, there is a problem in that the third party STAs over-protectthe TXOP.

FIG. 24 illustrates over-protection of a TXOP duration.

Referring to FIG. 24, an AP (e.g., a TXOP holder) transmits a DL MU PPDUframe. An HE-SIG A field of the DL MU PPDU frame includes a TXOP fieldand a MAC header field of the DL MU PPDU frame includes a durationfield. It is assumed that the duration field of the MAC header fielduses a granularity of 1 μs, whereas the TXOP field of the HE-SIG A fielduses a granularity of N μs. N is a natural number larger than 1.

STAs (e.g., TXOP responders) that are designated as recipients of the DLMU PPDU frame transmit a UL MU BA frame as a response to reception ofthe DL MU PPDU frame in a TXOP duration. It is assumed that anadditional frame is not subsequently transmitted by the AP (e.g., TXOPholder) and the STAs (e.g., TXOP responders) (e.g., TXOP termination).

STAs (e.g., third party STAs) that are not designated as the recipientsof the DL MU PPDU frame cannot decode a MAC header. Therefore, the thirdparty STAs set/update a NAV through the TXOP duration field of theHE-SIG A field. The STAs (e.g., third party STAs) set the NAV to a valueof the TXOP duration field of the HE-SIG A field included in the DL MUPPDU frame transmitted by the AP. In some cases, the STAs (e.g., thirdparty STAs) may update the NAV to the value of the TXOP duration fieldof the HE-SIG A field of the UL MU BA frame (e.g., when a TXOP durationvalue larger than a current NAV value is signaled).

Herein, since the NAV value set by the TXOP duration field of the HE-SIGA field is larger than an actual TXOP duration, over-protectioncorresponding to the difference between the NAV value and the TXOPduration occurs. The STAs (e.g., third party STAs) cannot access achannel during a time duration corresponding to over-protection.

To solve such a problem, information for early termination of a TXOP maybe transmitted. For example, the TXOP holder/responder may transmitinformation indicating that early termination is performed in a lastframe upon transmitting the last frame (e.g., ACK, Block ACK, orMulti-STA BA) during a TXOP duration. TXOP early termination may bereferred to as TXOP truncation or simplified to (early)termination/truncation. Hereinafter, methods of terminating the TXOPwill be described.

(1) Method Using CF-END Frame

The TXOP holder/responder may terminate the TXOP by transmitting aCF-END frame after transmitting the last frame during the TXOP duration.

(2) Method Using Early Termination Indicator

According to an embodiment, an STA may transmit an early terminationindicator in a part of a frame (e.g., a common part etc. of HE-SIG A orHE-SIG B). For example, if the early termination indicator is set to 1,this may indicate that the TXOP is terminated early. The TXOP may beimmediately terminated after a frame including the early terminationindicator set to 1.

Meanwhile, the early termination indicator may be used by being combinedwith a duration field. For example, if early termination indicator=1,this may indicate that the TXOP is terminated at a time indicated by theduration field. If the duration field is set to 0, this may indicatethat the TXOP is terminated after the corresponding frame. If theduration field is set to a value larger than 0, this may indicate thatthe TXOP is terminated at a time indicated by the duration field.

The term “early termination indicator” may be simply referred to as atermination indicator or a truncation indicator. While the earlytermination indicator may be explicitly signaled by the HE-SIG A field(e.g., a specific bit in the HE-SIG A field is set to the earlytermination indicator), the early termination indicator may beimplicitly signaled. As an example of implicit signaling, if the TXOPduration field in HE-SIG A indicates a specific TXOP value, this may beinterpreted as termination of the TXOP.

(i) a more data (MD) field or an ESOP field may be reused as the TXOPearly termination indicator.

(ii) In a DL frame, the early termination indicator may be transmittedthrough the last frame of a set TXOP. For example, the TXOP duration maybe updated and transmitted in the last frame, together with the earlytermination indicator. The TXOP duration may be set to a value smallerthan a legacy TXOP duration and termination of the TXOP may be indicatedthrough the early termination indicator.

(iii) When a frame is transmitted, if TXOP information needs to beupdated, an STA (e.g., a TXOP holder/responder) transmits the frame bysetting the frame to an updated TXOP. In the frame in which the TXOP isupdated, the early termination indicator is used as a TXOP updateindicator. For example, whenever the TXOP is updated, the earlytermination indicator may be set to 1 and transmitted. Upon receiving aframe in which the early termination indicator is set to 1, an STA(e.g., a third party STA) updates a TXOP of a corresponding STA (e.g.,NAV update).

(iv) In the case of single-frame (e.g., PPDU) transmission, the TXOPduration may be set to the size of an ACK/BA frame. In the case ofmulti-frame transmission, the TXOP duration may be set to a duration fortransmission of multi-frame and ACK/BA transmission.

(v) UL MU transmission: If a trigger frame is transmitted in a non-HTPPDU (e.g., 11a format), since the contents of the trigger frameaccurately indicate the TXOP duration, even a legacy STA (e.g., an STAnot supporting 11ax) may correctly set the TXOP duration (e.g., NAVsetting/update). In addition, since a UL MU frame indicates the TXOPduration corresponding to the transmission length of the ACK/BA frame,NAV setting/update is not problematic.

However, if an 11ax format is used and the TXOP duration set in HE-SIG Ais different from TXOP duration information (e.g., a TXOP duration of aMAC header) included in frame contents, NAV setting/update isproblematic. For example, partial STAs (e.g., third party STAs) may readonly the HE-SIG A field and other STAs (e.g., third party STAs) may readboth the HE-SIG A field and the frame contents.

The STAs that have read both the HE-SIG A field and the frame contentsset the TXOP through duration information of the frame contents (e.g.,MAC header). For example, the STAs that have read both the HE-SIG Afield and the frame contents contain the duration information includedin the HE-SIG A field. Once the STAs read the duration of the MAC header(or duration of the contents), the STAs determine a final TXOP durationbased on the duration of the MAC header (or duration of the contents)instead of the duration of the HE-SIG A field and update a NAV.

The STAs that have read only the HE-SIG A field update the NAV based onthe TXOP duration included in the HE-SIG A field. Even in this case,setting the TXOP duration to be longer than the TXOP duration of the MACheader may be problematic. For example, when an ACK/BA/M-BA frame forthe UL MU frame is transmitted, the STAs may update the TXOP throughTXOP duration information included in the HE-SIG A/B frame or the MACheader (e.g., NAV update) but terminate the TXOP at a corresponding timeif the early termination indicator (or TXOP update indicator) is set to1.

(vi) Meanwhile, TXOP termination may be performed based on a BSS color.For example, an STA (e.g., third party STA) may be configured toterminate the TXOP only when TXOP termination is indicated through aframe corresponding to my BSS color. The STA (e.g., third party STA)confirms the BSS color included in a frame. If the BSS color indicatesother BSSs, the STA (e.g., third party STA) does not terminate the TXOPeven when the corresponding frame indicates TXOP termination.Accordingly, the STA (e.g., third party STA) may terminate/truncate theTXOP only when a frame of my BSS color indicates TXOP termination (e.g.,through an explicit indicator, or implicit indication in which aduration is set to 0). However, loss of an access opportunity of acorresponding STA for other BSSs may occur.

(vi) According to an embodiment, an STA (e.g., a TXOP holder/responder)may necessarily transmit TXOP termination/truncation information in thelast frame upon transmitting an 11ax frame in the TXOP. Meanwhile, in an11a frame, since the TXOP is set through the duration of the MAC header,the TXOP can be accurately set. According to an embodiment, the durationof the MAC header may be overwritten into the TXOP duration of theHE-SIG A field.

(3) Method Using Value of TXOP Duration Field of HE-SIG A Field

According to an embodiment, an STA (e.g., a TXOP holder/responder) mayindicate TXOP early termination/truncation by setting the value of aduration field of a frame (e.g., the last frame transmitted in the TXOP)to a specific value (e.g., to 0 or by setting all bits to 1), instead ofusing an explicit TXOP termination indicator. Therefore, upon receivinga frame indicating Duration =specific value (e.g., 0), an STA (e.g., athird party STA) may determine that the TXOP duration isterminated/truncated after the corresponding frame. This may beappreciated as a role similar to a CF-END frame.

FIG. 25 illustrates TXOP truncation according to an embodiment of thepresent invention. For example, FIG. 25 illustrates a method for solvingan over-protection problem illustrated in FIG. 24 and a repetitivedescription in FIG. 24 will be omitted herein.

Referring to FIG. 25, a TXOP duration of an HE-SIG A field of a UL MU BAframe (e.g., the last frame transmitted in a TXOP) is set to 0. TXOPduration =0 may mean the TXOP is truncated.

An STA (e.g., a third party STA) acquires the value of a TXOP durationfield by decoding the HE-SIG A field of the UL MU BA frame. TheSTA(e.g., third party STA) confirms that TXOP duration =0 and resets acurrently set NAV (e.g., a NAV set through a DL MU PPDU frame) (e.g.,the NAV is set to 0).

According to a legacy NAV management operation, if currently set NAV≥received TXOP duration value, the STA does not update or reset the NAV.However, according to the present embodiment, upon receiving the TXOPduration set to 0, the STA resets the NAV even if currently set NAV>0.Accordingly, a time corresponding to over-protection can be efficientlyeliminated from the TXOP duration.

(4) NAV Management Method

According to a legacy NAV setting/update method, NAV update has beenperformed only when a TXOP duration value of a received frame is largerthan a currently set NAV value in an STA (e.g., a third party STA). ForTXOP early termination, the NAV needs to be updated even when the TXOPduration value of the received frame is smaller than the currently setNAV value in the STA. According to an embodiment, the STA may update theNAV to a TXOP duration smaller than the currently set NAV value in theSTA, based on the above-described TXOP truncation/termination/updateindicator. However, update of the NAV to the TXOP duration smaller thanthe currently set NAV value may be configured to be performed based onlyon a TXOP truncation/termination/update indicator included in my BSSframe.

Meanwhile, the STA may set and maintain the NAV on a BSS color basis.For example, upon receiving a frame indicating TXOP truncation, the STAthat has set the NAV on a BSS color basis may truncate the TXOP of theNAV corresponding to a BSS color indicated by the received frame.

To reduce complexity of NAV setting and management, the STA may set andmaintain two NAVs, i.e., a NAV of my BSS and a NAV of other BSSs (e.g.,BSSs other than my BSS or a frame which does not indicate my BSS). Theterm “NAV of my BSS” may be referred to an intra-BSS.

Operation of Power Saving (PS) Mode

Embodiment 1 of PS Mode Operation

An operation for TXOP power saving may be defined. For example, if apartial field of a frame (e.g., a partial field in HE-SIG A/B or anA-MPDU/MPDU/MAC header or a new field) indicates that the NAV can beupdated, the STA (e.g., third party STA) maintains a wake-up state. If apartial field of a frame indicates that there is no NAV update, the STAmay transition to a PS mode. To this end, an STA (e.g., TXOPholder/responder) for setting a TXOP may transmit, in a frame,information as to whether or not the NAV is updated later. The STA(e.g., third party STA) may transition to the PS mode, only when thereceived frame is my BSS frame and the received frame indicates that theSTA should transition to the PS mode (e.g., indicates that there is noNAV update). If the STA (e.g., TXOP holder/responder) for setting theTXOP indicates that the TXOP/NAV is to be updated, through transmissionof the frame, the STA (e.g., TXOP holder/responder) may not indicatethat the STA (e.g., third party STA) should transition to the PS modeand, only when the NAV is not to be updated, the STA (e.g., TXOPholder/responder) may indicate that the STA (e.g., third party STA)should transition to the PS mode. Even when an indication oftransitioning to the PS mode is provided, if DL data is present, the STA(e.g., third party STA) may not transition to the PS mode (i.e., dozestate).

Embodiment 2 of PS Mode Operation

According to an embodiment of the present invention, a UL MU protocolsuch as UL OFDMA or UL MU MIMO may be used in order to raise MACefficiency. A UL MU PPDU may be transmitted as an immediate response(e.g., SIFS, PIFS, etc.) to a trigger frame transmitted by an AP. The APmay allocate an MU resource to a plurality of STAs by includinginformation such as an STA ID and a Resource Unit (RU) in the triggerframe.

FIG. 26 illustrates an exemplary transmission of multiple UL MU framesin one TXOP.

An AP may receive multiple UL MU frames in one TXOP. For example, the APmay allocate a UL MU transmission resource to multiple STAs in one TXOPby transmitting trigger frames. In this embodiment, it is assumed thatSTAs STA1 to STA4 to which a resource is allocated through each triggerframe are maintained in the same state during the TXOP.

FIG. 27 illustrates another exemplary transmission of multiple UL MUframes in one TXOP.

In FIG. 27, it is assumed that STAs to which a resource is allocatedthrough each trigger frame vary during a TXOP.

As illustrated in FIG. 27, if STAs to which a resource is allocatedthrough each trigger frame vary, the STAs should confirm whether a ULresource allocated thereto is present whenever the trigger frame isreceived. If there is no resource allocated to the STAs, it may beappreciated that power consumed when the STAs receive the trigger frameis wasted.

An embodiment of the present invention proposes a method of reducingpower consumption of STAs in UL MU transmission.

Upon receiving a trigger frame, an STA confirms whether a resource isallocated thereto through the trigger frame (e.g., through BSS ID andSTA AID/address information). If the trigger frame does not includeaddress/ID information of the STA, the STA may transition to a dozestate during a specific duration (e.g., based on a UL PPDU duration).The specific duration may be set by the STA based on the UL PPDUduration.

For example, the specific duration may be one of (i) a UL PPDU duration(e.g., indicated by the trigger frame), (ii) SIFS+UL PPDU duration,(iii) SIFS+UL PPDU duration+SIFS, and (iv) SIFS+UL PPDUduration+SIFS+ACK (e.g., one of ACK/BA/M-BA) transmission times.However, the present invention is not limited thereto.

FIG. 28 illustrates a doze state of an STA based on a trigger frame.

Referring to FIG. 28, an AP allocates a UL MU resource to STA1 and STA2through a trigger frame. STA3 and STA4 receive the trigger frame andconfirm that resource allocation information allocated thereto is notpresent. Accordingly, STA3 and STA4 may transition to a doze state untilthe next UL PPDU duration.

Meanwhile, upon transmitting the trigger frame, the AP may transmit a PSmode field in the trigger frame.

The PS mode field may be a 1-bit indicator indicating a PS modeoperation.

For example, the PS mode field may indicate whether STAs to which aresource is not allocated through the trigger frame should transition toa doze state for power saving during a UL PPDU duration (or UL PPDUduration+ACK/BA/M-BA duration, which is assumed to be the UL PPDUduration for convenience) (e.g., PS mode field=0) or the STAs shouldtransition to the doze state for power saving during a TXOP duration(e.g., PS mode field=1). For instance, if the PS mode field is set to 0,this may indicate that the STAs should transition to the doze modeduring a corresponding UL PPDU duration in the TXOP duration and, if thePS mode field is set to 1, this may indicate that the STAs shouldtransition to the doze mode during the entire TXOP duration includingthe UL PPDU duration.

Accordingly, STAs, which have received the trigger frame but to which aUL MU resource is not allocated, confirm a PS mode included in the PSmode field. If “PS mode=0” is indicated, the STAs may enter the dozestate during the UL MU PPDU duration and, if “PS mode=1” is indicated,the STAs may enter the doze state during the entire TXOP duration. Ifthe AP allocates a UL MU resource to STAs of the same group (or a subsetof STAs of the same group) during one TXOP (e.g., if a group of STAs towhich a resource is allocated does not vary during the TXOP), the PSmode may be set to 1. Unlike this, if the AP allocates the UL MUresource to STAs belonging to different groups during the TXOP, the PSmode in the trigger frame may be set to 0. The PS mode field may bereferred to as a same STA group indication (0 for indication ofdifferent groups and 1 for indication of the same group) but the presentinvention is not limited thereto.

FIG. 29 illustrate a PS mode set to 0 (PS mode=0).

Referring to FIG. 29, since the PS mode is set to 0, STAs that do notinclude UL resource allocation information thereof in a trigger frametransition to a doze state until a UL PPDU duration.

STA1 and STA2 to which a UL resource is allocated through all triggerframes maintain an awake state.

STA3 and STA4 to which a UL resource is allocated only through the firsttrigger frame maintain an awake state during the first UL MU PPDUduration but transition to a doze state during the second and third ULMU PPDU durations.

STA5 to STA8 maintain an awake state during UL MU PPDU durations duringwhich STA5 to STA8 transmit UL MU PPDUs but transition to a doze stateduring the other UL MU PPDU durations.

The other STAs to which no resource is allocated through the triggerframe transition to the doze state during all UL MU PPUU durations.

For convenience of description, it has been assumed that a time lengthduring which an STA enters the doze state by the PS mode set to 0 is aUL MU PPDU duration. However, the present invention is not limitedthereto and the doze state may be maintained during other time lengths,for example, during a UL PPDU+ACK/BA/M-BA duration.

FIG. 30 illustrates a PS mode set to 1 (PS mode=1).

Referring to FIG. 30, since the PS mode is set to 1, STAs except forSTA1 to STA4 may transition to a doze state after receiving the firsttrigger frame. For example, it may be assumed that, if the PS mode isset to 1 and a UL resource is not allocated to an STA in the firsttrigger frame, the UL resource is not allocated to the STA even in thenext trigger frames transmitted during a TXOP.

Meanwhile, since the UL MU resource is not allocated to STA3 and STA4 inthe third frame, STA3 and STA4 may transition to a doze state during theremaining TXOP duration.

If a TXOP duration (or a duration field in a MAC header) is not includedin a trigger frame, a duration during which an STA operates in a PS mode(e.g., a time during which an STA operates in a doze mode) may betransmitted through the trigger frame and the duration during which anSTA operates in a PS mode may be used instead of the TXOP duration.

FIG. 31 illustrates a PS mode operating method according to anembodiment of the present invention. A repetitive description givenabove will be omitted herein.

Referring to FIG. 31, STA1 sets a PS mode field included in a triggerframe (S3105).

STA1 transmits trigger frame 1 including the PS mode field (S3120). Itis assumed that Trigger frame 1 does not allocate a resource for UL MUPPDU transmission to STA2 and allocates the resource for UL MU PPDUtransmission to STA3.

STA2 determines whether to transition to a doze state based on triggerframe 1. For convenience, it is assumed that STA2 transitions to a dozemode (S3125). For example, if the resource is not allocated to STA2through trigger frame 1, STA2 may determine to transition to the dozestate. A time during which STA 2 operates in the doze state may bedetermined based on the PS mode field included in trigger frame 1.

The PS mode field may indicate whether an STA operates in the doze stateduring the entire TXOP duration indicated by trigger frame 1 (e.g., PSmode=1) or operates in the doze state only during a durationcorresponding to a UL MU PPDU transmitted through the resource allocatedby trigger frame 1(e.g., PS mode=0). For example, if the PS mode fieldindicates that a corresponding STA should operate in the doze state onlyduring a duration corresponding to the UL MU PPDU, STA2 may transitionto an awake state after the duration corresponding to the UL MU PPDU inorder to receive trigger frame 2 transmitted after the durationcorresponding to the UL MU PPDU.

If the PS mode field indicates that a corresponding STA should operatein the doze state during the entire TXOP duration, STA2 may assume thatthe resource is not allocated thereto even through trigger frame 2transmitted after the duration corresponding to the UL MU PPDU.

A time during which STA2 operates in the doze state may be any one of aTXOP duration, a duration for a UL MU PPDU, and the sum of the durationfor the UL MU PPDU and a duration for an ACK frame for the UL MU PPDU.

The PS mode field may indicate whether a group of STAs to which theresource is allocated is maintained at the same state or the group ofthe STAs can be changed, during the corresponding TXOP duration.

FIG. 32 is an explanatory diagram of apparatuses for implementing theaforementioned method.

A wireless device 800 and a wireless device 850 in FIG. 32 maycorrespond to the aforementioned specific STA and AP, respectively.

The STA 800 may include a processor 810, a memory 820, and a transceiver830 and the AP 850 may include a processor 860, a memory 870, and atransceiver 860. The transceivers 830 and 880 may transmit/receive awireless signal and may be implemented in a physical layer of IEEE802.11/3GPP. The processors 810 and 860 are implemented in a physicallayer and/or a MAC layer and are connected to the transceivers 830 and880. The processors 810 and 860 may perform the above-described UL MUscheduling procedure.

The processors 810 and 860 and/or the transceivers 830 and 880 mayinclude an Application-Specific Integrated Circuit (ASIC), a chipset, alogical circuit, and/or a data processor. The memories 820 and 870 mayinclude a Read-Only Memory (ROM), a Random Access Memory (RAM), a flashmemory, a memory card, a storage medium, and/or a storage unit. If anexample is performed by software, the above-described method may beexecuted in the form of a module (e.g., a process or a function)performing the above-described function. The module may be stored in thememories 820 and 870 and executed by the processors 810 and 860. Thememories 820 and 870 may be located at the interior or exterior of theprocessors 810 and 860 and may be connected to the processors 810 and860 via known means.

The detailed description of the preferred examples of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred examples, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention described in the appended claims. Accordingly, the inventionshould not be limited to the specific examples described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

INDUSTRIAL APPLICABILITY

The present invention has been described on the assumption that thepresent invention is applied to a wireless LAN system supporting HEPPDUs. However, the present invention is not limited thereto and can beapplied to various wireless communication systems including IEEE 802.11.

The invention claimed is:
 1. A method of operating in a power saving(PS) mode by a station (STA) in a wireless Local Area Network (LAN)system supporting a High Efficiency Physical Layer Protocol Data Unit(HE PPDU), the method comprising: receiving a trigger frame forallocating a resource for transmission of an Uplink Multi-User (UL MU)PPDU; and determining whether to transition to a doze state based on thetrigger frame, wherein the STA determines to transition to the dozestate when the resource is not allocated to the STA through the triggerframe, wherein a time during which the STA operates in the doze state isdetermined based on a PS mode field included in the trigger frame, andwherein the PS mode field indicates whether the STA should operate inthe doze state during an entire transmission opportunity (TXOP) durationindicated by the trigger frame or the STA should operate in the dozestate only during a duration corresponding to the UL MU PPDU transmittedbased on the trigger frame.
 2. The method according to claim 1, whereinif the PS mode field indicates that the STA should operate in the dozestate only during the duration corresponding to the UL MU PPDU, the STAtransitions to an awake state after the duration corresponding to the ULMU PPDU in order to receive other trigger frames transmitted after theduration corresponding to the UL MU PPDU.
 3. The method according toclaim 1, wherein if the PS mode field indicates that the STA shouldoperate in the doze state during the entire TXOP duration, the STAassumes that a resource is not to be allocated to the STA even by othertrigger frames transmitted after the duration corresponding to the UL MUPPDU.
 4. The method according to claim 1, wherein the time during whichthe STA operates in the doze state is any one of the TXOP durationindicated by the trigger frame, a-the duration corresponding to the ULMU PPDU, and a sum of the duration corresponding to the UL MU PPDU and aduration for an acknowledgement response frame for the UL MU PPDU. 5.The method according to claim 1, wherein the PS mode field indicateswhether a group of STAs to which a resource is allocated is identicallymaintained or the group of the STAs is changed, during the TXOPduration.
 6. A station (STA) for operating in a power saving (PS) modein a wireless Local Area Network (LAN) system supporting High EfficiencyPhysical Layer Protocol Data Unit (HE PPDU), the STA comprising: areceiver configured to receive a trigger frame for allocating a resourcefor transmission of an Uplink Multi-User (UL MU) PPDU; and a processorconfigured to determine whether to transition to a doze state based onthe trigger frame, wherein the processor determines to transition to thedoze state when a resource is not allocated to the STA through thetrigger frame, wherein a time during which the STA operates in the dozestate is determined based on a PS mode field included in the triggerframe, and wherein the PS mode field indicates whether the STA shouldoperate in the doze state during an entire transmission opportunity(TXOP) duration indicated by the trigger frame or the STA should operatein the doze state only during a duration corresponding to the UL MU PPDUtransmitted based on the trigger frame.